The valve is equipped with a fusible metalsafety plug and a safety disc to release thecontents of the cylinder if the pressure becomesexcessive because of high temperatures. The safetyplug is filled with a fusible metal designed to meltat temperatures ranging from 208° to 220°F(97.8° to 104.5°C).The cylinder and valve assembly is connectedto the oxygen tubing by silver soldering thetubing to a coupling nose and securing the noseto the valve outlet with a coupling nut.The self-opening (automatic) oxygen cylindervalve is automatically opened when it is connectedto the oxygen line. The use of this type of valvepermits remote location of the oxygen cylinder toplaces less vulnerable during combat and morereadily accessible for servicing.RegulatorsThe success or failure of high-altitude flightdepends primarily on the proper functioning ofthe oxygen breathing regulator. Acting as a meter-ing device, the regulator is the heart of theoxygen system. To perform successfully in an air-craft system, a regulator must deliver the life-supporting oxygen in the quantities demandedthroughout its entire range of operation.Although personnel of the PR rating areprimarily responsible for maintenance ofregulators, the AME is responsible for per-forming operational checks in the aircraft and forremoval and installation. In other words, theAME removes a malfunctioning regulator fromthe aircraft and delivers it to the shop where thePR determines the trouble and makes thenecessary repairs. When the trouble is corrected,the AME reinstalls the regulator in the aircraft.TubingTwo types of tubing are used in aircraftoxygen systems. Low-pressure aluminum alloytubing is used in lines carrying pressures up to450 psi. High-pressure copper tubing is used inlines carrying pressure above 450 psi.NOTE: Some of the newer naval aircraft areequipped with high-pressure oxygen lines madeof aluminum alloy.Lines running from the filler valve to each ofthe cylinders are called filler lines. Thoserunning from the cylinders to the regulators arecalled distribution or supply lines.Oxygen lines, like all other lines in the aircraft,are identified by strips of colored tape. The stripsof tape are wrapped around each line near eachfitting and at least once in each compartmentthrough which the line runs. The color code foroxygen lines is green and white with the wordsBreathing Oxygen printed in the green portion,while black outlines of rectangles appear in thewhite portion.Resistance to fatigue failure is an importantfactor in oxygen line design because the linepressure in a high-pressure system will at timesexceed 1,800 psi, and at other times be as low as300 psi. Because of these varying pressures andtemperatures, expansion and contraction occur allthe time. These fluctuations cause metalfatigue, which must be guarded against in boththe design and the construction specifications fortubing. Steps are taken during installation toprevent fatigue failure of the tubing. Tubing isbent in smooth coils wherever it is connected toan inflexible object, like a cylinder or a regulator.Every precaution is taken to prevent the accidentaldischarge of compressed oxygen because of faultytubing or installation. Although simple in con-struction and purpose, tubing is the primarymeans by which oxygen is routed from thecylinders to the regulator stations.High-pressure tubing is usually seamlesscopper tubing, and is manufactured in accordancewith strict specifications. It has an outsidediameter of 3/16 inch and a wall thickness of0.035 inch. For application in high-pressureoxygen installations, copper tubing is type N (softannealed), and is pressure tested at not less than3,000 psi.High-pressure tubing is used between theoxygen cylinder valve and the filler connection inall systems, between the cylinder valve and theregulator inlet in high-pressure systems, andbetween the cylinder valve and pressure reducerin reduced high-pressure systems.To connect high-pressure copper tubing,adapters and fittings are silver soldered to thetubing ends. Due to the high pressures involved,the security (leak tightness) of all high-pressurelines relies primarily on a metal-to-metal contactof all its fittings and connections. A fittingproperly silver soldered to the end of a length ofcopper tubing will not come loose or leak.Some of the later models of naval aircraft usealuminum alloy or stainless steel tubing in high--pressure oxygen system installations. Replacementtubing should be manufactured of the same type4-6